The present invention relates to a hybrid magnetic bubble memory device in which magnetic bubble propagation tracks formed of an ion-implanted layer and magnetic bubble propagation tracks formed of a soft magnetic material film (for example, a nickel-iron alloy film such as a Permalloy film) are both provided on a single chip including a magnetic medium for supporting a magnetic bubble, and more particularly to the junctions of the two magnetic bubble propagation tracks.
Magnetic bubble propagation tracks formed of a Permalloy film (namely, Permalloy tracks) have hitherto been used in magnetic bubble memory devices. However, when these Permalloy tracks have a period of less than 4 .mu.m to be used in a high density device, the propagation margin of the tracks is too small for practical use. Meanwhile, it has been known that even when magnetic bubble propagation tracks formed by ion implantation have a period of less than 4 .mu.m, the propagation tracks can propagate magentic bubbles and moreover the propagation margin of these tracks is of practical values.
The magnetic bubble propagation tracks based upon ion implantation (namely, ion-implanted tracks) are formed in the following manner. As shown in FIG. 1, a contiguous-disc pattern 2 is first formed of a metal or photoresist film, on a magnetic bubble supporting layer 1 which is provided on a non-magnetic garnet substrate and made of magnetic garnet. Then, ions 3 such as Ne.sup.+ and H.sub.2.sup.+ are implanted in the surface of the bubble supporting layer 1 while using the pattern 2 as a mark. Thus, a layer of magnetization aligned in plane is formed of an ion-implanted layer 4, in a surface portion of the bubble supporting layer 1 on the outside of the pattern 2. A magnetic bubble 6 is propagated along the periphery of the pattern 2, namely, the boundary 5 of the ion-implanted layer 4. In the case where the bubble propagation tracks are formed in the above-mentioned manner, in order to suppress the generation of hard magnetic bubbles, an ion-implanted layer is previously formed in the whole surface of the bubble supporting layer 1 so that the depth of this ion-implanted layer is smaller than that of the ion-implanted layer 4 for forming the bubble propagation tracks.
The pattern 2 for determining the ion-implanted tracks 5 can be readily formed, since the pattern 2 is continuous, that is, has no gap between discs. Further, the ion-implanted tracks 5 have an advantage that a driving magnetic field for propagating a magnetic bubble can be made small. However, the ion-implanted tracks 5 have a drawback that when function parts necessary for a magnetic bubble memory device such as transfer gates and replicate gates are formed in the ion-implanted tracks 5, these function parts are small in operation margin or do not operate at all. Accordingly, the ion-implanted tracks 5 are not yet put into practical use. On the contrary, the above-mentioned function parts in the Permalloy tracks can perform a stable operation for practical use, and have a wide operation margin.
In view of the above facts, a hybrid magnetic bubble memory device has been developed in which the ion-implanted tracks are used in a memory part which is required to have a high density, and the Permalloy tracks are used in function parts (refer to a Japanese Patent Application Laid-Open No. 40791/1982, laid-open on Mar. 6, 1982, the application filed in the name of Fujitsu, Ltd.).
In the hybrid magnetic bubble memory device, it is desirable to avoid implanting ions in that portion of the bubble supporting layer which exists beneath the Permalloy tracks, to such a depth as required in forming the ion-implanted tracks. That is, when a layer of magnetization aligned in plane is formed below the Permalloy propagation tracks by ion implantation, the action of a magnetic pole which is produced in the Permalloy propagation tracks, on a magnetic bubble is weakened by the layer of magnetization aligned in plane, and thus the propagation margin is decreased. Accordingly, in ordinary cases, a thin ion-implanted layer is previously formed in the whole surface of the bubble supporting layer to suppress the generation of hard magnetic bubbles.
In the hybrid magnetic bubble memory device, it is important to appropriately determine the structure of the junction of the ion-implanted tracks and Permalloy tracks, in order to transfer a magnetic bubble between these propagation tracks smoothly.
In the above-mentioned Japanese Patent Application Laid-Open publication it is described that magnetic bubbles can be smoothly transferred between the ion-implanted tracks and the Permalloy tracks by overlapping two kinds of propagation tracks at their junction. However, the above Laid-Open publication does not disclose any detailed structure of the junction. The present inventors' experimental results have shown that a favorable propagation margin is not obtained only by overlapping two kinds of propagation tracks at the junction, but special attention has to be paid to the shape of the junction to obtain the favorable propagation margin.